A known liquid ejection apparatus, e.g., an inkjet printer, includes an ink ejection head including a plurality of piezoelectric element units. In the inkjet printer, each of the piezoelectric element units of the ink ejection head includes a polarized piezoelectric element. A drive voltage is applied to the piezoelectric elements to drive the piezoelectric elements. Thus, ink is ejected from the ink ejection head onto a recording medium. When the drive voltage is applied to the piezoelectric elements for a long period of time, for example, to print on a large number of recording mediums, the degree of polarization of the piezoelectric elements may be reduced, and the piezoelectric elements may deteriorate. When a printing operation is not performed, an electrical connection between electrodes that sandwich the piezoelectric elements may be disconnected to control reduction of the degree of polarization.
During a printing operation, the drive voltage is continuously applied to the piezoelectric elements even when they are not driven, because the electrical connection between electrodes, which sandwich the piezoelectric elements, is connected. Accordingly, the piezoelectric elements may deteriorate. Exceptional research of the present inventor finds that electrical disconnection, in a printing operation, between the electrodes, which sandwich the piezoelectric elements that are not driven, may reduce deterioration of the piezoelectric elements thereby contributing to longer operating life of the ink ejection head. However, this may lead to differences between the piezoelectric elements with respect to the degree of deterioration. Accordingly, the drive voltage applied to the piezoelectric elements needs to be adjusted based on the degree of their deterioration. If the differences among the piezoelectric elements with respect to the degrees of the deterioration increase, the range of adjustment of the drive voltage may increase. This may lead to breakage of a power circuit for supplying the drive voltage.
For example, print heads are connected to linear regulators in a voltage supply circuit for supplying drive voltage to the print head. The linear regulator is configured to output a drive voltage from an OUT terminal by reducing a main voltage input from an IN terminal. A switching regulator supplies the same main voltage to each linear regulator. To adjust the drive voltage for each print head, a voltage reduction range (regulated width) of each of the linear regulators is controlled. However, if differences of the drive voltage among the print heads, i.e., differences of the voltage reduction range of the linear regulators, increase, the voltage reduction range of the linear regulator corresponding to the minimum drive voltage may increase. Accordingly, a heating amount of the linear regulator corresponding to the minimum drive voltage may become relatively large, and the voltage supply circuit may be damaged.